1. The Field of the Invention
The present invention relates to systems and methods for improving vascular blood flow, and more specifically (A) for improving arterial blood flow in the lower extremities by (a) increasing venous blood flow and (b) enhancing functionality of the vessels with high shear rates through compression of specific portions of the foot, ankle, and calf of a patient, and (B) for reducing the incidence of venous blood clot formation in the lower limbs by creating pulsatile venous flow and promoting venous emptying.
2. The Relevant Technology
Improvement of arterial blood flow in patients with obstructions of the arteries to the leg is usually obtained by surgically bypassing the occluded arteries, or by removing obstructions with devices that are inserted into the blood vessel. In elderly patients who have undergone multiple vascular procedures, the deterioration of arterial blood flow can lead to severe pain (ischemic neuritis), tissue loss (arterial ulcers), or toe loss (gangrene). When the arteries cannot be repaired anymore, this situation may lead to leg amputation.
In order to increase vascular blood flow without surgery, devices are sometimes used which apply a compressive force to various designated areas of the foot or leg. This compressive force is designed to increase the amount of blood returning to the heart through the veins, thereby increasing the arterial blood flow to the extremity. These compressive forces are typically designed to mimic a walking action which helps to push blood through the veins to the heart.
In normal walking, the foot is intermittently weight bearing, a result of which is to flatten the plantar arch. This flattening motion causes a spreading force between the ball and heel of the foot and a squeezing of the sole of the foot. This action produces a foot-pump action that helps to increase the venous blood flow in the leg. Prior art devices have therefore focused on mimicking such a flattening of the plantar arch. This is usually performed by wrapping a bladder completely around the foot between the heel and the ball of the foot. A fluid is then injected into the bladder in order to create a compressive force both on the top and bottom of the foot. Such an approach, however, creates several problems.
Devices that compress the feet of certain sensitive patient groups, such as diabetics, may irritate the skin and ultimately lead to skin breakdown over the bony areas at the midtarsal region. The compression of this midtarsal region thus leads to a situation where compression therapy for a particular class of patients must be limited in duration in order to avoid such tissue breakdown. It would, therefore, be advantageous to allow compression therapy of this class of patients over a longer period of time without breakdown of the skin over the bony areas at the midtarsal region.
In addition to the breakdown of tissue over the midtarsal region for certain groups of patients, prior art devices also are not usable on that portion of the patient population which have abnormally shaped feet. For certain patients, a bladder which completely encircles the foot and extends in a region from about the heel to the ball of the foot will not fit. It would, therefore, be advantageous to allow compression therapy on a wide range of patients including those having abnormal foot shapes.
For certain patients who have extremely sensitive feet, the application of a compressive force on both the top and bottom of the foot can cause tremendous pain. Patients who have had reduced blood flow in the lower extremities for a long period of time are especially susceptible to pain when compression therapy of the foot is initiated. It would, therefore, be advantageous to allow for a treatment regime which gradually increases a patient's tolerance until compression therapy of the foot can be tolerated.
Finally, because the bladder completely encircles the foot, it can be difficult to assess the effectiveness of the treatment or to identify any developing problems. Since the bladder covers almost the entire foot, visual inspection can be difficult. Often to assess the effectiveness and identify developing problems, the treatment must be stopped and the device removed. It would, therefore, represent an advancement in the art to allow increased visual inspection during treatment with little or no impact on the effectiveness of the treatment.
Another problem suffered by patients is deep vein thrombosis. Deep vein thrombosis (DVT) is the formation of thrombus in the deep veins of the lower limb. DVT may follow trauma or surgery and is often associated with activated blood clotting factors and/or very slow blood flow called stasis. External pneumatic compression prevents stasis by two possible mechanism types: (1) a small volume of blood is accelerated to a relatively high velocity for a short period of time, and a large volume of blood is accelerated to a relatively low velocity for a longer period of time. Foot compression devices such as that described by Cook in U.S. Pat. No. 5,354,260 are examples of the first type in that the relatively small foot blood volume is accelerated rapidly to a high velocity. Calf and thigh compression devices such as that described by Hasty in U.S. Pat. No. 4,013,069 are examples of the second type in that a large blood volume in the calf and thigh are accelerated to relatively lower velocities for periods of time that typically exceed that of foot only compression types.
Since foot only compression does not significantly effect flow in some of the large veins in the calf (such as the so-called soleal sinuses where thrombi often originate), calf vein thrombi are still a large potential problem. Calf and thigh compression may move larger amounts of blood but stasis is better reduced with high blood velocities. It would, therefore, be desirable to be able to both create high blood velocities and move large blood volumes to provide patients with prophylaxis against deep vein thrombosis.